1. Field of the Invention
This invention relates generally to magnetic recording disks, and more particularly to a disk with patterned nondata islands for head-positioning and data synchronization.
2. Description of the Related Art
Conventional continuous-media (CM) disks have a continuous layer of magnetic material that becomes formed into concentric data tracks containing the magnetically recorded data bits when the write head writes on the magnetic material. A variation of a CM disk is a “discrete-track media” (DTM) disk, meaning that the concentric data tracks of continuous magnetic material are radially separated from one another by concentric nonmagnetic guard bands. Bit-patterned-media (BPM) disks have been proposed to increase the data density. In a BPM disk, the magnetic recording layer on the disk is pre-patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. In one type of patterned media, the islands are elevated regions or pillars that extend above the spaces and magnetic material covers both the islands and the spaces, but the spaces are far enough from the read/write head to not adversely affect reading or writing, so the spaces can be considered essentially nonmagnetic. Alternatively, the patterned media may be fabricated so that that there is no magnetic material in the spaces between the islands. One method proposed for making BPM disks is by nanoimprinting from a master template.
CM disks, DTM disks and BPM disks all require nondata regions that are used for read/write head positioning and data synchronization. BPM disks typically have nondata regions that are also pre-patterned, meaning that there are nondata islands separated by nonmagnetic spaces. CM disks and DTM disks may also have pre-patterned nondata regions. The proposed method for formatting disks with pre-patterned nondata regions is to DC “erase” the disk during manufacturing with a large magnet, leaving all of the nondata islands magnetized in the same direction. Thus all of the nondata islands would have a magnetization direction either “into” or “out of” the surface of the disk. However, because only a single polarity of magnetization is used with this method, half of the available signal amplitude from the nondata islands is sacrificed and thus the signal-to-noise ratio (SNR) is less than optimum.
What is needed is a recording disk with patterned nondata islands that have alternating polarity of magnetization to provide optimal SNR, and a relatively fast and low-cost method for magnetizing the nondata islands with the proper polarity.